Yeast-like fungi

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FUNGI



Candidosis

Sour Crop - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath
  • Candidia albicans is the most important species
    • C. tropicalis and C. pelliculosa are other important species
  • World wide distribution
  • Usually an endogenous mycoses
  • Noramlly present on skin, vagina and in the GI tract
  • Immunocompromised animals may show symptoms
  • Usually lesions on mucous membranes and at mucocutaneous junctions
  • Many species have been implicated in bovine mastitis
  • C. albicans has been isolated in porcine stomach ulcers
  • C. rugosa has been implicated in pyometra in mares
  • Infection of the crop, oesophagus and mouth occur in poultry and other birds leading to sour crop
    • White-grey lesions in mouth which adhere loosly to the mucous membrane
    • Crop wall may be thickened
    • Crop wall may be covered by a yellow-white necrotic material
    • Underlying tissue is inflammed
  • Causes thrush in humans
  • C. albicans causes metritis and vaginitis in mares and genital candidiosis in stallions (and bulls)
  • Skin scrapings in 20% KOH for microscopy
  • Diphtheritic membranes, pus and fluids can be examined by Lactophenol Cotton Blue and stained by Gram or Methylene Blue
  • Gram positive, oval, thin-walled budding cells with hyphal fragments
  • Grow on blood agar and Sabouraud's Dextrose agar producing soft, creamy colonies in 24-48 hours
  • Grossly:
    • Exudative, papular, pustular to ulcerative dermatitis
    • Stomatitis and otitis externa may develop
  • Microscopically:
    • Spongiotic neutrophilic pustular inflammation
    • Parakeratosis
    • Ulcerations
    • Superficial exudate containing organisms

Cryptococcosis

  • Over 19 species
    • C. neoformans only major pathogen
  • Worldwide
  • Occurs in high concentrations in pigeon droppings (high creatinine concentration)
    • The pigeon is not infected
    • C. neoformis colonise the droppings after they have been excreted
    • Also found in fruit, milk and soil
  • Exogenous, inhaled infection which is generally sporadic (non-contageous)
    • Can also be absorbed via skin penetration and ingestion
  • May be a primary pathogen or opportunistic
  • Targets the respiratory system
    • Including the paranasal sinuses
    • Also can be systemic, cutaneous, visceral, skeletal or ocular
  • Causes sporadic mastitis in cattle
    • Can spread within the herd
  • Affects the CNS of dogs and cats
    • Paranasal sinuses and pharynx can be infected with dissemination to the CNS and other tissues
      • E.g. Lungs, kidneys and joints
    • Also causes subcutaneous granulomas
    • The tip of the nose is a common site of infection in cats
  • Causes myxoma-like lesions of the lung and lip in horses
  • Causes cryptococcal meningitis in humans
  • Also affects dolphins, foxes, ferrets, monkeys, birds, cheetahs and guinea-pigs
  • Large yeast with capsule seen using India ink stain
  • Stains with PAS (Periodic acis Schiff)
  • Gram positive
  • Grows on blood agar and Sabouraud's Dextrose agar forming white, granular colonies which become slimy, mucoid and turn cream/brown within a week
  • Species identified by carbohydrate assimilation tests
  • Antigen and antibody should be tested for as antibody formed by the body is soon overwhelmed and neutralised by abundent polysaccharide antigen from the capsule, in active, systemic infections
    • Latex agglutination for antigen, complement fixation, ELISA and IFAT can be used

Geotrichosis

  • G. candidum
  • Rare
  • Two forms: the yeast-like (glaborous) and fluffy
  • Affects a wide range of species
  • Usually diagnosed post-mortem
  • Affects the mucous membranes, udder, bronchi and lungs
  • Usually mild, causing suppurative granulomas
  • Can be recovered from otitis externa infections in dogs
  • Organisms appear as rectangular or spherical arthrospores on wet mounts
    • Thick walled, non-budding, gram positive
  • Grow on Sabouraud's Dextrose agar
    • Membranous colonies
    • Does not grow well on blood agar

Malassezia pachydermidis

Malassezia pachydermidis - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath
  • Normally present in oily areas on the external ear canal and skin in dogs
    • Some strains have been recovered from the ear canal of cats
  • Bottle-shaped, small budding cells, non-mycelial
  • Gram stain shows purple yeast cells with a very wide base
  • Grow on Sabouraud's Dextrose agar in 2 weeks of incubation at room temperature
  • Greenish discolouration on blood agar
  • Clinical disease may cause yeast to proliferate and cause infection
  • Grossly:
    • Regional lesions: muzzle, ears, interdigital, perianal
    • Or generalised disease
    • Erythematous, hyperpigmented, lichenified and scaly lesions with alopecia
  • Microscopically:

Rhodotorula

  • Rhodotorula minuta and R. rubra
  • Canine ear infections
  • Equine uterus
  • Seldom seen in animal infections

Torulopsis glabrata

  • Commensal in animals and is found in the soil
  • Implicated in cases of:
    • Pyelonephritis, pneumonia, septicaemia and meningitis (humans)
    • Mastitis and abortion in cattle
    • Systemic infection of monkeys and dogs

Trichosporonosis

  • Found in soil
  • Deuteromycetes yeast
  • Trichosporonosis beigelii
    • Implicated in feline nasal granuloma, skin infections in horses and monkeys, mastitis in cattle and sheep and in feline bladder infections
  • T. capitum implicated in bovine mastitis

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